Fix repeated block param

Co-Authored-By: Matt Valentine-House <matt@eightbitraptor.com>

prism_compile.c

@@ -6399,6 +6399,12 @@ pm_compile_node(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *const ret,
             table_size++;
         }
 
+        if (parameters_node && parameters_node->block) {
+            if (PM_NODE_FLAG_P(parameters_node->block, PM_PARAMETER_FLAGS_REPEATED_PARAMETER)) {
+                table_size++;
+            }
+        }
+
         // When we have a `...` as the keyword_rest, it's a forwarding_parameter_node and
         // we need to leave space for 2 more locals on the locals table (`*` and `&`)
         if (parameters_node && parameters_node->keyword_rest &&
@@ -6747,14 +6753,20 @@ pm_compile_node(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *const ret,
                 body->param.flags.has_block = true;
 
                 pm_constant_id_t name = ((pm_block_parameter_node_t *)parameters_node->block)->name;
+
                 if (name == 0) {
                     local_table_for_iseq->ids[local_index] = PM_CONSTANT_AND;
                     st_insert(index_lookup_table, PM_CONSTANT_AND, local_index);
                 }
                 else {
-                    pm_insert_local_index(name, local_index, index_lookup_table, local_table_for_iseq, scope_node);
+                    if (PM_NODE_FLAG_P(parameters_node->block, PM_PARAMETER_FLAGS_REPEATED_PARAMETER)) {
+                        ID local = pm_constant_id_lookup(scope_node, name);
+                        local_table_for_iseq->ids[local_index] = local;
+                    }
+                    else {
+                        pm_insert_local_index(name, local_index, index_lookup_table, local_table_for_iseq, scope_node);
+                    }
                 }
-
                 local_index++;
             }
         }

test/ruby/test_compile_prism.rb

@@ -1545,6 +1545,10 @@ a
       CODE
     end
 
+    def test_repeated_block_underscore
+      assert_prism_eval("def self.m(_, **_, &_); _; end; method(:m).parameters")
+    end
+
     def test_repeated_kw_rest_underscore
       assert_prism_eval("def self.m(_, **_); _; end; method(:m).parameters")
     end